The present invention relates generally to current sensing devices for electrical systems, and more particularly to automatically resettable alternating current fault indicators for use within closed housings such as are utilized to enclose pad-mounted components in an underground power distribution system.
Various types of fault indicators have been constructed for detecting electrical faults in power distribution systems, including clamp-on type fault indicators, which clamp directly over cables in the systems, and test-point type fault indicators, which are mounted over test points in cables or associated connectors of the systems. Such fault indicators may be either of the manually reset type, wherein it is necessary that the indicators be physically reset, or of the self-resetting type, wherein a fault indication is reset upon resotration of line current. Examples of such fault indicators are found in products manufactured by E. O. Schweitzer Manufacturing Co. of Mundelein, Ill., in U.S. Pat. Nos. 3,676,740, 3,906,477 and 4,063,171 of the present inventor, and in the copending application of the present inventor, Ser. No. 958,103, filed Nov. 6, 1978.
Detection of fault currents by self-resetting fault indicators is often accomplished by means of a reed switch located within the indicator housing having contacts in close proximity to the conductor being monitored. Upon occurrence of an abnormally high fault-associated magnetic field around the conductor, the contacts close and actuate circuitry which magnetizes an internal pole piece to position to a trip position a target indicator visible from the exterior of the indicator. Upon restoration of current in the conductor another circuit is actuated to reposition the target indicator to a reset or non-fault indicating position.
With the increased use of underground electrical distribution system wherein primary and secondary feeder cables are directly buried in the ground, and are brought to the surface only for connection to pad mounted distribution transformers or other system components, the need has arisen for fault detectors suitable for mounting within the above-ground metal enclosures typically utilized to house and protect such components. Preferably, such fault indicators should be sufficiently compact so as to not interfere with other components in the enclosures, and should not compromise the security provided to the power system components by the enclosures against vandalism or theft.
It has been found that those fault indicators which provide a visible indication of fault occurrence, such as by rotation of an indicator flag or by the flashing of a light, and therefore require that a window or other opening by provided in the housing, tent to attract the interest of vandals, and to provide encouragement for those seeking access to the enclosure, increasing the possibility of damage to the enclosure from attempted entry.
The present application is directed to a fault indicator for use within an equipment enclosure wherein fault indications are provided at a magnetic test point external to the enclosure, thereby obviating the need for visual contact with the interior of the enclosure.
Accordingly, it is a general object of the present invention to provide a new and improved fault indicator for use in conjunction with enclosed pad-mounted power distribution system components.
It is a more specific object of the present invention to provide a compact and economical fault indicator which provides an indication of circuit status at a remote magnetic test point.